Análisis del nivel de cumplimiento en el marco de la Ley General del Ambiente

Dielectric measurements were caixied out at Strathclyde University at both high and low frequencies; however, only the low frequency results are quoted here. The high frequency results had errors that could not be corrected by scaling and the opinion was offered by the tester that "they would be so hedged around with qualifications as to be useless", apparently due to the dimensions of the samples available.

Four polymers, viz. POL.TEEC/TGC.O, POL.TEEC.IO, POL.TEEC.25 and POL.TEEC.50, were tested across a low frequency range. This was in an attempt to reveal any trends which might be induced by the increase in the proportion of epoxy functionalised cyanurate in the monomer mixture.

Fig. 4.41 (below) shows that all four polymers show a similar pattern of decreasing dielectric constant with increasing frequency. All three TEEC-containing polymers have significantly lower dielectric constants (irrespective of frequency) than POL.TEEC/TGC.O, the cyanurate-free analogue.

However, as can be seen in Fig. 4.42 (below), they are not in the expected order, which was that the greater the amount of cyanurate the lower the dielectric constant. Why POL.TEEC.IO should have lowest dielectric constant is not readily apparent.

Fig. 4.41 4.5 - 4 - 4 2 0 2 4 6

□

O O A POL.TEEC/TGC.O POL.TEEC.IO POL.TEEC.25 POL.TEEC.50 log Frequency Fig. 4.42 4 4 - 3 0 10 20 30 40 50 60 TEEC %TEEC

The values for dielectric constant in Fig. 4.42 (above) are taken arbitrarily from the highest frequency measurement (frequency = 63 kHz, log frequency = 4.8) for the purposes of examining the trend. (The actual values being less important than the trend.) However, it must be emphasised that this trend might change at higher frequencies, so care must be taken not to draw too many firm conclusions.

All four polymers also show a dispersion amplitude at around 1 Hz (log frequency = 0) (Fig. 4.41). This is due to a relaxation in the chemical structure of the polymer at this frequency. It can also be seen that this relaxation is less pronounced for POL.TEEC.IO than for the others. It is likely that this is a short-range relaxation rather than the long-range bulk relaxation of the polymer. It seems that there is something anomalous about POL.TEEC.IO that makes its dielectric characteristics different from what would be expected, although it should be noted that it does not give anomalous results in the testing of other properties.

Fig. 4.43

□

O

o

A POL.TEEC/TGC.O POL.TEEC.IO POL.TEEC.25 POL.TEEC.50 log Frequency

Dielectric loss measurements show a peak at around 1 Hz (log frequency = 0) (Fig. 4.43 above). This is due to the same relaxation shown by the dispersion amplitudes in the dielectric constant plots.

Fig. 4.44 0.2 - 0.15 -

I

□

o

O A POL.TEEC/TGC.O POL.TEEC.IO POL.TEEC.25 POL.TEEC.50 0.05 - log Frequency

Fig. 4.44 (above) is an expanded version of Fig. 4.43 (above). The reason that the points below log frequency = 0 are very scattered is due to the fact that the limits of the

experiment have been exceeded. It can be seen that, unlike the dielectric constant graphs, the dielectric loss graphs actually cross so it is not sufficient just to pick one frequency at which to correlate the four polymers' dielectric loss with their TEEC content. Fig. 4.45 (below) shows dielectric losses measured at frequency 25 Hz (log frequency = 1.4) and Fig. 4.46 (below) shows dielectric losses measured at frequency 63 kHz (log frequency = 4.8).

Fig. 4.45 0.075 - 0.05 - •c

□

TEEC 0.025 - Fig. 4.46 %TEEC 0.2 0.175 •c Q 0.15 -

□

_TEEC 0.125 - %TEEC

Once more a general trend is observed, with dielectric loss decreasing with the amount of cyanurate monomer included, but again POL.TEEC.IO stands out as an anomaly, even if less so at higher frequencies. However, the objective set out at the start has been fulfilled, in that in this polymer system the dielectric properties of an epoxy resin can be improved by incorporating a degree of cyanate ester resin character through inclusion of some cyanurate-containing structural units.

4.3 Experimental

4.3.1 Monomer synthesis

Eugenol epoxide

Eugenol epoxide had previously been synthesised on a small scale by reaction of m-chloroperoxybenzoic acid (MCPBA) with eugenol^^, the work-up using potassium

fluoride to precipitate any MCPBA or m-chlorobenzoic acid left. Purification was by preparative thin layer chromatography but no yields are mentioned. It was felt that this route was not desirable due to the use of potassium fluoride which would lead to the production of hydrogen fluoride and that the purification by preparative thin layer chromatography would not be ideal when comparatively large amounts of product are required.

MCPBA oxidations of double bonds are well known and the following procedure (outlined in Fig. 4.47 below) was based on one of these.

Fig. 4.47

MCPBA _► HO

MeO

Eugenol (60 g, 0.36 mol) was dissolved in dry dichloromethane (-100 cm^). 55% MCPBA (200 g, 0.64 mol) was dissolved in dichloromethane and the solution then washed with water. The dichloromethane layer was separated and dried (MgSO^). The dry solution of MCPBA in dichloromethane was then slowly added to the eugenol solution over 2 h keeping the temperature below 20°C. The mixture was stirred at room temperature for 48 h, then filtered to remove the m-chlorobenzoic acid that had

precipitated out. Excess peroxy-acid was destroyed by washing with 10% sodium metabisulfite solution, and this was followed by further washing with 10% sodium

bicarbonate solution and saturated sodium chloride solution and drying over MgS0 4.

The solvent was then evaporated off to leave a reddish liquid. Due to the reactive nature of the epoxy group it was not feasible to purify the product by distillation so column chromatography on silica gel was preferred. A 4 : 1 mixture of petroleum (b.p. 40- 60°C) and diethyl ether was used as eluant, the first fraction being identified as unreacted eugenol. Once the epoxy eugenol fraction started to come off the colmnn, the mixture proportions were changed to 7 : 3 petroleum to diethyl ether. This resulted in a yellow liquid; yield 37 g (56%). Ôy (CDCI3) 2.56 (IH, dd, H J, 2.79 - 2.83 (3H, m,

CH2 + Hb), 3.12 - 3.16 (IH, m, H J, 3.87 (3H, s, OMe), 5.72 (IH, hr s, OH), 6.72 -

6.76 (2H, m, Ar-H), 6.83 - 6.87' (IH, m, Ar-H). 7a,b = *^b,c ==-^CH2,c 5.1; 4,c 2.6*.

ÔC 38.4 (j), 46.9 (i), 52.8 (h), 55.9 (g), 111.6 (f), 114.4 (c), 121.6 (b), 129.0 (a), 144.4 (d) and 146.5 (e).

Other reaction conditions were used: increased temperature, various reaction times and different excesses of MCPBA, but these led to decreased yields of eugenol epoxide, with either less eugenol being used up or the epoxide ring-opening products being obtained.

Tris(epoxyeugenyl) cyanurate (TEEC)

This method was adapted from a synthesis of the unepoxidised analogue in a European patent application^?.

Eugenol epoxide (18.55 g, 0.104 mol) and cyanuric chloride (6.08 g, 0.033 mol) were dissolved in acetone (-75 cm^) and sodium hydroxide (3.95 g, 0.100 mol) in water (50 cm^) slowly added without allowing the temperature to rise above 10“C. The mixture was then stirred for 1 h, extracted with dichloromethane and the extract dried

(MgS0 4). On evaporation of the solvent a clear viscous liquid was obtained. This

liquid was induced to recrystallise by heating with methanol, to give rosette-like

crystals, m.p. 132-134“C. Yield 17.02 g (85%). (Found: C, 64.3; H, 5.4; N, 7.0. C33H33N3O9 requires C, 64.4; H, 5.4; N, 6.8%.) ôy (CDCI3) 2.56 (IH, dd, H J,

2.79 - 2.83 (3H, m, CH2 + Hy), 3.12 - 3.16 (IH, m, H J, 3.74 (3H, s, OMe), 6.78 -

6.82 (2H, m, Ar-H) and 7.01 - 7.05 (IH, m, Ar-H). CE2,c^‘^’ *^a,c ^ 6. (The assignments of the resonances of H^, Hy, H^ and the CH2 group, and the

coupling constants, were assigned by a series of decoupling experiments.) 38.4 (j), 46.6 (i), 52.1 (h), 56.6 (g), 113.3 (f), 120.8 (c), 122.0 (b), 136.3 (a), 139.2 (d), 150.8 (e) and 173.5 (k). Fig. 4.48 3 HO MeO Cl

A

base Hg

:

a

:

Triglycidyl cyanurate (TGC) Fig. 4.49 3 base Cl Cl

l i t

_{N Cl} O

o

N " ^ N

The method (adapted from a U.S. patent^^) for this reaction is similar to that for TEEC above, with a reaction mixture of glycidol (132 g, 1.78 mol), cyanuric chloride (100 g, 0.54 mol) in acetone (250 cm^) and sodium hydroxide (67 g, 1.675 mol) in water (100 cm^). The product is a viscous liquid and although literature references say it should be a white solid of low m.p., after chilling in diethyl ether, (softening at 30°C, completely melted at 53-60°C) l^C n.m.r. showed that only very minor impurities were present and that further purification was unnecessary. Yield 146 g (91%). ôy (CDCI3)

2.73 (IH, dd, Ha), 2.89 (IH, dd, Hy), 3.38 - 3.42 (IH, m, H Jt, 4.31 (IH, dd) and 4.70 (IH, dd, CH2). ÔC 43.7 (d), 48.3 (c), 68.3 (b) and 172.1 (a).

4.3,2 Polymer synthesis

The following polymers were all prepared as 6 x 4 inch panels in polished metal

moulds. The moulds were sprayed with a release agent such as 'Frekote' to allow easy removal of the panels from the moulds. The moulds were also levelled in the curing oven, using a spirit level, to ensure that the panels would have an even thickness. The monomer mixtures were prepaied by dissolving the reactants (total mass 100 g) in the

appropriate hot solvent and reducing the volume so that it would all fit in the mould.

4.3.2.1 Standard polymers

Standard polymers were prepared using the manufacturer's data sheets for cure schedules.

POL.STA.1

XU 71787 cyanate ester prepolymer (Fig. 4.50) manufactured by Dow was dissolved in hot acetone and copper(II) acetylacetonate / nonylphenol catalyst (2.6 g) added. This catalyst was prepared by mixing copper(II) acetylacetonate (1 g) in nonylphenol (100 g) at 135°C for 1 h. This mixture was poured into the mould in an oven preheated to 110“C. A vacuum was carefully applied, under which conditions the acetone bubbled off. When no more degassing was observed (~ 1 h) the vacuum was released and the temperature increased to IIT C and the mixture allowed to cure at that temperature for 2 h. The black polymer was then allowed to cool in the mould slowly overnight. Once the polymer panel had been removed from the mould it was post-cured for a further 2 h at 232“C.

Fig. 4.50

OCN OCN OCN

POL.STA.2

934 Epoxy (100 g), a commercially popular epoxy resin system which includes curing agents, hardeners and other additives as well as epoxy monomers, was dissolved in hot acetone. It was poured into the mould at 110°C and degassed under vacuum. The vacuum was released and the polymer cured for 2 h at 177°C.

POL.STA.3

Bisphenol A dicyanate (Fig. 4.51) (97.4 g) was dissolved in hot acetone and 2.6 g of the copper(II) acetylacetonate catalyst described in the synthesis of POL.STA.l added. The solution was poured into the mould and degassed under vacuum at 100°C. As the solvent evaporated off the bisphenol A dicyanate crystallised out before melting later. With the vacuum released the material was cured at 177°C for 4 h. After cooling slowly overnight the polymer panel was removed from the mould and post-cured for 2

h at 240“C. Fig. 4.51

CHg ^

In document Análisis Jurídico de la Ejecución Presupuestaria de los Proyectos de Inversión Pública Elaborados para la Descontaminación del Río Chili, en el Marco del SNIP, Provincia de Arequipa, 2016 (página 93-109)